1. Field of the Invention
The present invention relates to a printing apparatus, a printing position adjustment value setting method and a printing method respectively designed so that the printing position adjusting pattern printed on each printing medium is scanned by an optical sensor to determine the adjusting value to be applied in adjusting the printing position.
2. Description of the Related Art
In recent years, with the spread of the personal computers and the digital cameras, the technologies relating to various printing apparatuses (the various types of printers) and the technologies for speeding the operation of such printing apparatuses and the technologies for obtaining the prints of higher quality have been developed rapidly. Among these printing apparatuses, the serial-type printing apparatus of a dot matrix printing method is coming to the fore as a printing apparatus capable of realizing the high-quality image printing at low cost and high speed. Among the printing methods adopted for such a high-speed printing, there is, for example, a 2-way printing method, while among the printing methods for the high-quality image printing, there is, for example, a multi-scanning printing method.
In the case of the dot matrix printing method, it is necessary to adjust the position for depositing the ink on the printing medium in order to obtain a high-quality printed image. Hence, the technology for the registration of the print (the printing position adjustment), that is, a technology of a dot alignment process for adjusting the deposit position of the ink is necessary. The dot alignment process is a process for determining the adjusting value for adjusting the position whereon the ink dot is to be deposited (i.e., the printing position) sometimes including the process for controlling the printing process while adjusting the printing position according to the determined adjusting value.
Conventionally, this kind of registration process in printing (i.e., the printing position adjustment) has been practiced as described in the following.
For instance, in the case of the 2-way printing method characterized by the forward and the backward scanning processes, the rule mark, as a position adjusting pattern, is printed on the printing medium so that the printing position adjusting value can be determined on the basis of the printing rule mark. More specifically, firstly the timing of the printing for the forward scanning and the timing for the backward scanning are adjusted to each other, and the relative position adjustment conditions between the forward scanning and the backward scanning are varied to print the rule marks on the printing medium. Each user or the operator (of the printing apparatus) observes the printed rule marks for the forward scanning and the backward scanning to select the optimal printing conditions for the best combination of the printing position during the forward scanning and the printing position during the backward scanning. Then, the optimal printing conditions are set with the printer or the host computer.
When using a plurality of printing heads for ejecting the printing inks respectively, the relative positions of the ink ejecting nozzles of different printing heads are determined as described in the following. First, the relative printing position adjustment conditions among different printing heads are varied (from one another) to print the rule marks, as being the printing position adjustment patterns. Each user or operator checks the printed rule marks to select the optimal (combination of) the printing conditions best matching with one another for the printing by the plurality of printing heads. Then, the optimal (combination of) the printing conditions are set with the printer or the host computer.
The Japanese Patent Application Laid-open No. 11-291470(1999) and the Japanese Patent Application Laid-open No. 11-291553(1999) disclose an automatic dot alignment process respectively. These processes are designed for automatically align the printing positions during the forward scanning of the printing head with the printing positions during the backward scanning of the printing head by using an optical sensor and without requiring the manual operation by the user or the operator. Further, the Japanese Patent Application Laid-open No. 11-291477(1999) discloses a structure for defining the relative positions of the printing head and the optical sensor in consideration of the processing time and the optical characteristic.
Such conventional printing position adjustment methods, however, require the user or the operator to select the printing position adjusting conditions by checking the result of the print and by following the cumbersome procedure in many instances. Thus, it is possible that the users who are not willing to follow such a cumbersome steps may use the printer even omitting the registration between the print made by the forward scan and the print made by the backward scan or omitting the correction of the disagreement among the prints made by a plurality of printing heads.
Further, in the case of the conventional print registration methods, the print registration conditions can be selected only from among those corresponding to the printed registration adjustment patterns. Thus, in order for the operator to seek the print registration of higher accuracy, for example, it is necessary to print as may number of patterns corresponding to finely varied print registration conditions as possible, so that the users are required to distinguish such fine differences of the patterns in selecting and setting desired print registration conditions. Such procedure may not be so cumbersome to the experienced users of the printing apparatuses, but it can be so cumbersome and time-consuming to the ordinary users thereby subjecting such users to some intolerable mental burden in the worst case.
On the other hand, when applying the automatic dot alignment process by using the optical sensor, firstly the adjustment patterns for the print registration are printed on the printing medium so as to be read out later by the optical sensor. Then, the best adjustment pattern for the best print registration needs to be determined. Hence, it is necessary that all of the necessary adjustment patterns be printed on the printing medium. Further, even where the adjustment patterns have been printed once, there occurs sometimes that the optical characteristic, such as the printing density of the adjustment pattern, cannot be read correctly depending on the condition of the printing medium thereby making it impossible to attain the desired dot alignment correctly. For instance, when the inkjet printing method, designed to eject the ink droplets from the printing head, the ink droplets are absorbed by the printing medium, so that there is the possibility that the shape of the printing medium varies in the process of drying. To be more specific, there can occur the cockling or the curling of the printing medium. In such an event, the optical characteristic of the printed adjustment pattern is subject to vary depending on the conditions wherein the printing operation takes place or the kind of the printing medium or the kind of ink to be used.